Process and apparatus for forming a gasket directly on a workpiece.

Abstract: A process and an apparatus for forming a gasket (12) directly on a workpiece (10) having a joining surface (14) which has an annular gasket-fixing groove (16), wherein a mold (20, 56, 66, 120) having a gasket-forming groove (26) which cooperates with the gasket-fixing groove to define a cavity (28) for forming the gasket (12) is clamped to the joining surface of the workpiece, and a material is injected into the cavity through an injection passage (34) which is formed through the mold and which communicates with the gasket-forming groove. The material is cured into the gasket, and the mold is removed from the workpiece. The mold may have two elastic sealing members (60, 62, 70, 72) disposed on inner and outer sides of the gasket-forming groove, respectively, so as to extend along the gasket-forming groove, and provide pressure-tight sealing of the cavity when the body is placed on the workpiece such that the sealing members are held in elastic pressure-tight contact with the joining surface.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for forming a gasket directly on a workpiece. The invention also relates to an apparatus suitable for practicing the above process. Discussion of the Related Art A gasket or elastically deformable packing is used to make a pressure-tight joint between stationary components such as a body of an engine and a head cover. For instance, such a gasket is attached to the joining surface of the head cover. Conventionally, a gasket produced independently of the head cover, typically, a commercially available gasket is fitted in a gasket-fixing groove formed in the joining surface of the head cover. Since the gasket is usually elastically deformable and flexible, it is difficult to automate the operation to attach the gasket, and the operation is performed manually by the worker. The manual attachment of the gasket to the workpiece suffers from a relatively large fluctuation in the condition of fitting of the gasket in the groove, and does not assure satisfactory pressure tightness at the joint. Techniques to simultaneously form and fix a gasket on the workpiece have been proposed. An example of such techniques is disclosed in document JP-A-5-5089, wherein two components or workpieces to be pressure-tightly joined together are assembled such that the joining surfaces define a space, and a suitable material is injected into the space, to form a gasket within the space. Document JP-A-1-295078 discloses another technique in which a gasket forming groove formed in a mold is filled with a resin material that expands upon curing thereof, and is placed on the workpiece, and the resin material is cured and expanded into a gasket fixed on the workpiece. Since these techniques permit simultaneous formation and fixing of a gasket on the workpiece, the procedure to attach the gasket to the workpiece is eliminated. In the technique disclosed in document JP-A-5-5089 in which the material is injected into the space formed between the joining surfaces of the assembled components or workpieces, it is impossible to check the formed gasket within the assembly, leading to relatively low forming stability or reliability of the gasket. Further, the size of the gasket cannot be larger than that of the space, resulting in insufficient pressure tightness at the joint and leading to a risk of development of a gap at the joint by vibration of the assembly. While the use of a material which expands upon curing thereof is possible, the gasket formed in this case contains a gas, and is not hard enough to assure a desired degree of pressure tightness at the joint. In the technique disclosed in document JP-A-1-295078, on the other hand, air is likely to be trapped in spaces between the material and the surfaces defining the gasket forming groove when the groove is filled with the material before the mold is placed on the workpiece. Further, air if contained in the material cannot be easily removed since the material generally has a high viscosity, and air voids or bubbles tend to exist in the formed gasket, causing a variation in the quality of the gasket. Another drawback of this technique arises from the use of a resin material which expands upon curing. Described more specifically, the gasket formed by expansion of the resin material so as to extend from the joining surface of the workpiece is considerably weak or soft, and does not provide a sufficient degree of pressure tightness at the joint with respect to another component even if the two components are clamped together so as to cause elastic deformation of the gasket. Further, the material is applied to the mold so as to fill the gasket forming groove. It is cumbersome and time-consuming to apply the material to the mold particularly where the gasket to be formed has a complicated three-dimensional configuration. A process and an apparatus comprising the features of the pre-characterizing portions of claims 1 and 4 are essentially known from document US-A-4 321 225. In this known gasket forming process, the gasket is formed directly on the joining surface of the workpiece such that the gasket is partly fixed in the gasket-fixing groove which cooperates with the gasket-forming groove of the mold to form the cavity corresponding to the gasket. Accordingly, this known process does not require a separate or independent step of attaching the gasket to the joining surface of the workpiece, contrary to the conventional process which includes a step of forming a gasket independently of the workpiece and a step of attaching the thus formed gasket to the workpiece. The gasket can be simultaneously formed and fixed on the workpiece, by clamping the mold to the joining surface of the workpiece, and injecting the suitable material into the cavity through the injection passage formed through the mold. The cavity can be easily and efficiently filled with the material, even where the gasket has a complicated three-dimensional configuration. This is not so in the conventional process in which the material is applied to the gasket-forming groove in the mold before the mold is placed on the workpiece. Further, this known process does not suffer from trapping of air within the material filling the cavity, and thus assures improved quality of the gasket formed of the air-free material. Since the mold has the gasket-forming groove which provides a part of the cavity, the gasket partly received and fixed in the gasket-fixing groove formed in the joining surface of the workpiece extends above the joining surface by an amount corresponding to the depth of the gasket-forming groove. Further, the material need not be expandable upon curing thereof. Therefore, the gasket formed on the workpiece provides a high degree of fluid tightness or pressure tightness when the workpiece and a mating component are clamped together during assembling such that the gasket is elastically compressed against the joining surface of the mating component. A process and an apparatus similar to the process and apparatus according to document US-A 4 321 225 are known from document US-A-2 995 057. Document EP-A-0 553 486 discloses a process and an apparatus for forming a workpiece by molding a polymeric material. The process according to this document comprises the step that an elastic tube is attached to a body of a mold such that the elastic tube communicates with a fluid passage of the body and is disposed on the outer side of a forming cavity so as to extend peripherally along the forming cavity. When the body is clamped to a joining surface of a second body of the mold, the elastic tube is held in elastic pressure-tight contact with the joining surface. A pressurized-fluid supply device is connected to the fluid passage for supplying the elastic tube with a pressurized fluid. The pressurized-fluid supply device of this known apparatus is provided with a pressure regulator comprising a timer by means of which the pressure of the pressurized fluid in the elastic tube can be controlled in dependence on various molding steps. The pressure control is effected such that the elastic tube is pressurized with a constant pressure after the mold has been closed and before the polymeric material is injected. Prior to the subsequent opening of the mold, the pressure inside the hollow elastic tube is released. Alternatively, the pressure in the elastic tube can be temporarily decreased after the injection of the material. Accordingly, in this known process and apparatus, the pressure of the pressurized fluid is controlled according to a predetermined pattern in dependence on time. SUMMARY OF THE INVENTION It is an object of the present invention to further develop the process according to the pre-characterizing portion of claim 1 such that it assures an improved pressure tightness at the joining surface of the workpiece with respect to the body of the mold. A further object of the present invention consists in further developing the apparatus according to the pre-characterizing portion of claim 4 such that it is suitable for practicing the process according to the invention. These objects are achieved by the process and the apparatus according to claims 1 and 4, respectively. In the process and apparatus according to the invention, the pressurized fluid is fed from the pressurized-fluid supply device into the elastic tubes through the fluid passage formed through the mold clamped to the workpiece, so that the elastic tubes inflated by the pressurized fluid provide pressure-tight sealing of the cavity on its inner and outer sides, while the material is injected by the material injecting device into the cavity through the injection passage. As a result, the gasket is simultaneously formed and fixed on the joining surface of the workpiece. Further, the inner and outer elastic tubes provide pressure-tight sealing of the cavity over the entire periphery and on the opposite sides of the cavity, without an excessive clamping force between the mold and workpiece, even where the joining surface of the workpiece has some strain, deflection or buckling, or a low degree of surface smoothness. Accordingly, the mold used in the present invention assures improved yield ratio of the material, and provides substantially the same advantage as described above with respect to the process and apparatus according to document US-A-4 321 225. On the other hand, it is noted that as the injection of the material progresses, the resistance to flow or injection of the material through the injection passage into the cavity increases, and the injection pressure of the material accordingly increases. An increase in the injection pressure tends to increase a gap or clearance between the mold and the workpiece, and is likely to cause leakage of the material from the cavity. In view of this tendency, it is provided that at least one of the pressurized-fluid supply device and the material feeding device is controlled such that the pressure of the pressurized fluid in the elastic tubes and the injection pressure of the material increase so as to maintain or satisfy a predetermined relationship without leakage of the material from the cavity. This arrangement is effective to prevent leakage of the material even in a latter half of the injection period during which the injection pressure of the material is relatively high. Further, the injection of the material can be initiated at a relatively early point of time at which the pressure of the fluid in the elastic tubes is comparatively low. That is, it is not necessary to start the injection of the material only after the pressure of the fluid in the elastic tubes has been raised to a considerably high level which corresponds to a high level of the injection pressure that is expected to be generated in the latter half or terminal portion of the injection period. This arrangement permits reduction of the non-productive time, resulting in reduced overall time required to form the gasket. The predetermined relationship indicated above between the pressure of the pressurized fluid and the injection pressure of the material can be determined by experiment, for example, on the basis of the required pressure levels of the pressurized fluid which do not cause leakage of the material at different levels of the injection pressure of the material, or on the basis of the allowable levels of the injection pressure which do not cause leakage of the material at different levels of the pressurized fluid pressure. These relationships obtained by experiment may be represented by data maps stored in a memory of the controller. In this case, the controller controls the pressurized-fluid supply device and/or the material feeding device according to the stored data maps. At least one of these devices may be controlled such that if the actual pressure of the pressurized fluid is lower than the required pressure level or if the actual injection pressure is higher than the allowable level, the delivery rate of the pressurized fluid of the pressurized-fluid supply device is increased, or the injection of the material by the feeding device is temporarily interrupted or the amount of the injection is reduced. In one advantageous arrangement of the apparatus according to the the invention, the controller comprises means for providing an indication of abnormality associated with the supplying of the elastic tubes with the pressurized fluid, if the pressure of the pressurized fluid detected by the first pressure sensor is lower than a predetermined threshold. In this preferred form of the apparatus, the operator is informed of the presence of any abnormality associated with the supply of the pressurized fluid into the elastic tubes, if the pressure of the pressurized fluid in the elastic tubes is lower than the predetermined threshold level. This arrangement therefore provides for early detection of abnormality such as damage of the elastic tubes or defective connection of the pressurized-fluid supply device to the mold, and is effective to prevent reduction of the yield ratio of the material and defective gasket due to leakage of the material from the cavity. The threshold level may be a fluid pressure level that permits normal injection of the material into the cavity. For instance, the actual pressure of the pressurized fluid is compared with the threshold level when a suitable time has passed after the injection of the material is initiated. The data map stored in the controller to control the pressurized-fluid supply device and/or the material feeding device may be used to compare the actual pressure of the pressurized fluid with the required pressure level indicated above. In this case, the indication of abnormality may be provided if the actual fluid pressure is held lower than the required level for more than a predetermined time, for example. BRIEF DESCRIPTION OF THE DRAWINGS The above and optional objects, features and advantages of the present invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings, in which: Figs. 1(a) through 1(e) are views indicating process steps in a process of forming a gasket on a subject component or workpiece according to one embodiment of the present invention; Fig. 2 is a front elevational view of an engine head cover as the workpiece on which the gasket is formed according to the method of Figs. 1(a)-1(e); Fig. 3 is a front elevational view of the head cover on which a mold for forming the gasket is superposed in the method of Fig. 1; Fig. 4 is a bottom plan view of the mold of Fig. 3; Fig. 5 is a cross sectional view taken along line 12-12 of Fig. 3; Fig. 6 is a schematic view illustrating a gasket fabricating system according to an embodiment of the invention; Figs. 7 and 8 are flow charts illustrating an operation of the gasket fabricating system of Fig. 6 in injecting a material into the mold; Fig. 9 is a graph indicating an example of a data map used in step S13 of Fig. 8 to calculate required air pressure PA2; and Fig. 10 is a front elevational view showing the mold to which an air bleeder joint is connected after the material is cured, in the gasket fabricating system of Fig. 6; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to Figs. 1(a) through 1(e), there will be briefly described process steps for eventually forming or fabricating a gasket 12 on a workpiece in the form of a head cover 10 of a motor engine, as shown in Fig. 2. The head cover 10 has a joining surface 14 at which the head cover is pressure-tightly fixed to the body of the engine. The joining surface 14 has a generally annular or closed-loop gasket-fixing groove 16 in which the gasket 12 is partly received. As indicated in Fig. 2, the gasket 12 is formed so as to partly extend above the joining surface 14. In the process step of Fig. 1(a), a mold 66 for forming the gasket 12 is placed on the joining surface 14 of the head cover 10, and the mold 66 and the head cover 10 are clamped together by a suitable fixture 22 under pressure. The fixture 22 is a clamping device for holding the mold 66 and the head cover 10 together without a gap therebetween in the following material injecting step of Fig. 1(b) and material firing or curing step of Fig. 1(c). For instance, the fixture 22 may consists of an internal force type clamping device such as a toggle clamp, and/or an external force type clamping device such as a hydraulic clamp adapted to hold the mold 66 in the material injection step of Fig. 1(a). Where the head cover 10 and mold 66 are moved from one station to another for the different process steps while being clamped together, it is desirable to use only the internal force type clamp. The mold 66 clamped to the head cover 10 in the clamping step of Fig. 1(a) is shown in Figs 3 and 4. The mold 66 has a joining surface 24 which is shown in the bottom plan view of the mold 66 in Fig. 4. The joining surfaces 14 and 24 of the head cover 10 and mold 66 are also shown in the cross sectional view of Fig. 5 taken along line 12-12 of Fig. 3. As is apparent from Figs. 3-5, the mold 66 has a gasket-forming groove 26 formed in its joining surface 24. The gasket-forming groove 26 cooperates with the gasket-fixing groove 16 to define a gasket-forming cavity 28 when the mold 66 is clamped to the head cover 10 in a predetermined relationship. The gasket-forming groove 26 has a cross sectional shape corresponding to the desired shape of the gasket 12 to be formed, more precisely, corresponding to the desired shape of a part of the gasket 12 which extends above the joining surface 14 of the head cover 10. In the present embodiment, the gasket-forming groove 26 has a substantially semicircular shape as seen in Fig. 5. The mold 66 has a plurality of positioning pins (not shown) formed on the joining surface 24, while the head cover 10 has corresponding pin holes (not shown) formed in the joining surface 14, so that the mold 66 and the head cover 10 are positioned relative to each other by engagement of these positioning pins and holes. The positioning holes may be the holes provided for engagement with positioning pins which are provided on the engine body for attaching the head cover 10 to the engine body with the gasket 12 interposed therebetween. Alternatively, the mold 66 may be formed for engagement with a peripheral portion of the head cover 10 for positioning of the mold 66 and head cover 10 relative to each other. Further, the fixture 22 may be adapted to position the mold 66 and head cover 10 relative to each other. The mold 66 has an injection passage 34 open to the gasket-forming groove 26, and a connector 38 attached thereto for communication with the passage 34, as indicated in Fig 4. The connector 38 has an inlet (not shown) at one end thereof remote from the outer end of the passage 34. Further details of the mold 66 will be described later. Referring back to Fig. 1(b), a material for forming the gasket 12 is injected into the cavity 28 through the passage 34 while the mold 66 is clamped to the head cover 10 by the fixture 22. To this end, a material feeding device 88 is connected to the connector 38, as shown in Fig. 6. The material feeding device 88 includes a connecting tube 42 for connection to the connector 38, a feed cylinder 46 for forcing the material (indicated at 44 in Fig. 6) into the connecting tube 42, and a pump 48 (pale pump) for delivering the material 44 from a suitable reservoir to the feed cylinder 46. The connecting tube 42 is adapted for pressure-tight or fluid-tight connection with the connector 38 with a suitable sealing member (e.g., rubber seal), by simply forcing the connecting tube 42 onto the connector 38. However, the tube 42 may be connected to the connector 38 by a mechanical device such as threaded members. The feed cylinder 46 has a piston 50 and is designed so that one movement of the piston 50 to its elevated position causes the material 44 to be fed by an amount necessary for fabricating one gasket 12, that is, for forming the gasket 12 on one workpiece (head cover 10). The piston 50 is activated by suitable drive means such as a motor 89 and a feed screw rotated by the motor 89, which are provided in the material feeding device 88. Alternatively, the piston 50 is reciprocated by a pneumatically or hydraulically operated cylinder (not shown) provided in the material feeding device 88. Further details of the gasket fabricating system 90 of Fig. 6 will be described later. The material 44 may be a liquid rubber material such as a liquid silicone rubber and a liquid acrylic rubber, which can be injected into the cavity 28 through the injection passage 34 and which can be cured into the gasket 12. In the step of Fig. 1(c), the material 44 injected into the cavity 28 is hardened or cured in a curing device 52. To this end, the head cover 10 and the mold 66 which are clamped together by the fixture 22 are disconnected from the material feeding device 88, and are introduced into the curing device 52. Since the material 44 has a comparatively high viscosity value, the material 44 will not be discharged from the cavity 28 through the injection passage 34 even after the connecting tube 42 is disconnected from the connector 38. The curing device 52 is designed depending upon the properties of the material 44 to be used. For example, the curing device 52 may be a hot-air furnace, a high-frequency heating device or a far-infrared heating device, where the material 44 is a heat-curable material, that is, curable by exposure to heat. Where the material 44 is a UV-curable material, that is, curable by exposure to ultraviolet radiation, a UV generator may be used as the curing device 52. Where the material 44 is heat-curable, the mold 66 is desirably formed of a heat-resistant metal or synthetic resin material. Where the material 44 is UV-curable, the mold 66 is desirably formed of an acrylic or polycarbonate resin, a glass or other material which transmits ultraviolet radiation. In the step of Fig. 1(d), the head cover 10 and the mold 66 are taken out of the curing device 52 after the material 44 has been cured, and the mold 66 is removed from the head cover 10 by operating the fixture 22 to its unclamping position. With the mold 66 removed from the head cover 10, the gasket 12 formed by curing the material 44 within the cavity 28 is partly exposed on the joining surface 14 of the head cover 10, while it is partly accommodated in the gasket-fixing groove 16. Thus, the head cover 10 with the gasket 12 formed on its joining surface 14 is obtained, as shown in Fig. 2. In this respect, it is noted that the gasket-fixing groove 16 is shaped for more difficult removal of the gasket 12 or material 44 from the groove 16 than from the gasket-forming groove 26 in the mold 66, and that the surface defining the groove 26 is coated with a suitable mold release agent for facilitating the removal of the material 44 therefrom. Therefore, the gasket 12 is retained on the head cover 10 when the mold 66 is removed from the head cover 10. The surface of the groove 26 in the removed mold 66 is coated with a mold release agent, and the mold is returned to the station of the mold clamping step of Fig. 1(a), while the head cover 10 with the gasket 12 formed thereon is cooled as needed, and moved to the next station in which the head cover 10 is subjected to another process step as indicated at Fig. 1(e). In the gasket fabricating process described above, the gasket 12 is fixed in the groove 16 in the head cover 10 while the gasket 16 is formed by the mold 66 placed on the head cover 10. Thus, it is not necessary to first fabricate a gasket separately from or independently of the head cover, and then attach the gasket to the head cover 10. That is, the present process does not require a separate cumbersome, time-consuming step of attaching the gasket 12 to the head cover 10. The gasket 12 is simultaneously formed and fixed on the joining surface 14 of the head cover 10, by simply clamping the mold 66 onto the head cover 10 and injecting the material 44 into the cavity 28 defined by the mold 66 and head cover 10. The present process permits easy and more efficient fabrication of the high-quality gasket 12 with improved stability without undesirable trapping of air within the material 44 during injection, even if the gasket 12 has a complicated three-dimensional configuration. Further, the gasket 12 partly accommodated in the fixing groove 16 formed in the head cover 10 is partly exposed extending from the joining surface 14 by a distance corresponding to the depth of the gasket-forming groove 26 formed in the mold 66. Accordingly, the material 44 of the gasket 12 need not be a material which expands upon curing thereof, and the exposed portion of the gasket 12 is elastically compressed upon attachment of the head cover 10 to the body of the engine, whereby a comparatively high degree of pressure tightness is obtained between the head cover 10 and the engine body. The present embodiment uses the mold 66 which includes a body 68, and elastic sealing members in the form of a pair of rubber tubes 70, 72 disposed on the joining surface 24 of the body 68. The body 68 has the gasket-forming groove 26, injection passage 34 and connector 38 as described above. The rubber tubes 70, 72 are partly received and bonded in respective inner and outer generally annular grooves formed along the groove 26 in the joining surface 24, as indicated in Fig. 4. The rubber tubes 70, 72 are adapted to be held in elastic pressure-tight contact with the joining surface 14 of the head cover 10, and cooperate with the head cover 10 to define the pressure-tight cavity 28. The material of the rubber tubes 70, 72 is selected so that the material of the rubber tubes 70, 72 does not disturb the curing of the material 44 and so that it has a sufficient heat resistance where the material 44 is heat-curable. Where the material 44 is a heat-curable liquid silicone rubber material, for example a fluoro rubber rubber containing fluorine is preferably used as the material of the rubber tubes 70, 72. Where the material 44 is a liquid acrylic rubber, an ordinary acrylic rubber or nitrile rubber may be used for the sealing rubber tubes 70, 72. To minimize an influence of the rubber tubes 70, 72 on the height and cross sectional shape of the gasket 12 to be formed, the rubber tubes 70, 72 should preferably be positioned and dimensioned as follows: The distance between the rubber tubes 70, 72 and the edge of the groove 26 should be about 1-2 mm. The distance of extension of the rubber tubes 70, 72 from the joining surface 24 before the mold 66 is clamped to the head cover 10 should be about 0.5 mm. The width of the rubber tubes 70, 72 at their lower end face should be about 2-3 mm. The two rubber tubes 70, 72 communicate with each other by two communication passages 74, 74 formed in the body 68. The outer rubber tube 72 communicates with a fluid passage 76 formed in the body 68, and the fluid passage 76 communicates with a connector 78 attached to the body 68. The rubber tubes 70, 72 have openings 80 at which the tubes 70, 72 are connected to the communication passages 74 and fluid passage 76. The connector 78 is connectable to a connecting tube 84 of a pressurized-fluid supply device 82 (air compressor) as shown in Fig. 6, and to an air bleeder joint 86 as shown in Fig. 10, for example. The connector 78 is designed to be open when it is connected to the connecting tube 84 or air bleeder joint 86, but closed when it is disconnected from the tube 84 or joint 86, so that the pressurized air introduced in the rubber tubes 70, 72 is held therein. The rubber tubes 70, 72 are elastically expanded by the pressurized air introduced therein, so that the expanded tubes 70, 72 are elastically forced against the joining surface 14 of the head cover 10. The number and position of the communication passages 74 connecting the inner and outer tubes 70, 72 may be changed as needed. The fluid passage 76 may be formed in communication with the communication passages 74. For instance, the mold 66 of Figs. 3-5 may be used in the gasket fabricating system 90 shown in Fig. 6, which is constructed according to an embodiment of the present invention. After the mold 66 is clamped to the head cover 10 by the fixture 22, the connecting tube 42 of the material feeding device 88 is connected to the connector 38 of the mold 66, while the connecting tube 84 of the pressurized-fluid supply device 82 is connected to the connector 78 of the mold 66. The motor 89 is controlled according to a drive signal received from a controller 92. The pressurized-fluid supply device 82 incorporates an air compressor which is controlled according to a drive signal received from the controller 92, so that the pressurized air as a pressurized fluid is fed into the rubber tubes 70, 72 through the connecting tube 84, connector 78 and fluid passage 76. To the connecting tube 42, there is connected a pressure sensor 94 for detecting an injection pressure PB of the material 44. To the connecting tube 84, there is connected a pressure sensor 96 for detecting the pressure PA of the compressed air in the rubber tubes 70, 72. Signals indicative of these pressures PB, PA are sent from the sensors 94, 96 to the controller 92. While the pressure detected by the pressure sensor 96 is the pressure within the connecting tube 84, this detected pressure can be used as the pressure PA within the rubber tubes 70, 72, since the pressure in the tubes 70, 72 is only slightly different from the pressure in the connecting tube 84. The pressure sensors 94, 96 may be thin-film type pressure sensors in which piezoelectric elements or strain gages are disposed on a thin film which deforms depending upon a pressure difference with respect to the atmospheric pressure. The pressurized-fluid supply device 82 may be adapted to pressurize a liquid or a gas other than the air. The material feeding device 88 using the motor 89 and feed screw to actuate the piston 50 of the feed cylinder 46 may be replaced by a material feeding device in which a hydraulically or pneumatically operated cylinder is used to move the piston 50 with a suitable back pressure. The controller 92 includes a microcomputer incorporating a central processing unit (CPU), a random-access memory (RAM), a read-only memory (ROM), input and output interface circuits, A/D converters, and a timer circuit such as a crystal or quartz oscillator. The CPU operates to process signals to control the material feeding device 88, pressurized-fluid supply device 82 and a display 98, according to control programs stored in the ROM while utilizing a temporary data storage function of the RAM. There will be described an operation of the gasket fabricating system 90 under the control of the controller 92, by reference to the flow chart of Figs. 7 and 8. When a start switch is turned on, the controller 92 starts executing a control routine illustrated in Figs. 7 and 8. The routine is initiated with step S1 to activate the pressurized-fluid supply device 82 to feed the compressed air to the rubber tubes 70, 72 at a predetermined delivery rate. Step S1 is followed by step S2 to read the air pressure PA represented by the signal from the pressure sensor 96. Then, the control flow goes to step S3 to determine whether the air pressure PA is equal to or higher than a predetermined initial level PA1. This initial level PA1 is determined by experiment or simulation or by calculation, on the basis of the actual air pressure in the rubber tubes 70, 72 when these tubes 70, 72 are normal, such that the initial level PA1 permits the rubber tubes 70, 72 to be expanded to an extent for sufficient pressure-tight contact with the joining surface 14 so as to prevent leakage of the material 44 injected. When the detected air pressure PA has been raised to the initial level PA1, the control flow goes to step S4. While the air pressure PA is lower than the initial level PA1, step S3 is followed by step S9 to increment a counter C1, and step S10 to determine whether the content of the counter C1 has reached a predetermined number N1. The counter C1 is initialized or reset to "0" immediately after the routine is started, and incremented each time step S9 is implemented. Steps S9 and S10 cooperate to detect an abnormally slow increase in the air pressure PA due to some trouble such as a damage of the rubber tubes 70, 72, a defect in the pressurized-fluid supply device 82, and defective connection of the connecting tube 84 and connector 78. The predetermined number N1 is determined by first determining an optimum number to be counted by the counter C1 during a time period required for the pressure PA to be raised to the initial level PA1. The optimum number is determined by experiment or simulation or by calculation on the basis of the delivery rate of the compressed air and the cycle time necessary to repeat steps S1-S3, S9 and S10 while the tubes 70, 72, device 82, connecting tube 84 and connector 78 are normal. The number N1 is determined to be larger than the thus determined optimum number by a suitable value that accommodates a possible variation. If a negative decision (NO) is obtained in step S10, the control flow goes back to step S1. If an affirmative decision (YES) is obtained in step S10, the control goes to step S11 to turn off the pressurized-fluid supply device 82, and to step S12 to turn on an ALARM light on the display 98, for indicating the operator of the system 90 of the presence of some abnormality associated with the supply of the compressed air into the rubber tubes 70, 72. If an affirmative decision (YES) is obtained in step S3 with the detected air pressure PA reaching the predetermined initial level before the content of the counter C1 reaching the predetermined number N1, the control flow goes to step S4 in which the motor 89 of the material feeding device 88 is turned on to start feeding the material 44. The motor 89 may be operated at a predetermined constant speed, or at a speed which varies with time according to a predetermined pattern so that the injection pressure PB of the material 44 increases with an increase in the compressed air pressure PA. Alternatively, the motor 89 may be operated with a suitable torque. The pressurized-fluid supply device 82 is kept operated to raise the air pressure PA in the rubber tubes 70, 72 even after the affirmative decision (YES) is obtained in step S3, namely, even after the injection of the material 44 is started in step S4. Step S4 is followed by step S5 to read the injection pressure PB of the material 44 represented by the signal received from the pressure sensor 94. Then, the control flow goes to step s6 to determine whether the detected injection pressure PB has reached a predetermined final level PB1. The injection pressure PB is initially comparatively low, and increases as the feeding resistance of the material 44 increases with an increase in the amount of injection of the material 44. The pressure PB suddenly rises when the cavity 28 is filled with the injected material 44. The final level PB1 is the pressure at which the cavity 28 is filled with the material 44. The final level PB1 is determined by experiment or simulation or by calculation. When the injection pressure PB has reached the final level PB1, step S7 is implemented to turn off the material feeding device 88 to stop the injection of the material 44, and turn off the pressurized-fluid supply device 82 to stop the supply of the compressed air. Step S7 is followed by step S8 to turn on a CAVITY FULL light on the display 98, to inform the operator of the completion of injection of the material 44 into the cavity 28. If a negative decision (NO) is obtained in step S6, that is, if the detected pressure PB is lower than the final level PB1, the control flow goes to step S13 (Fig. 8) to calculate a required air pressure level PA2, on the basis of the injection pressure PB detected in step S5, and according to a stored data map or equation representative of a predetermined relationship between PB and PA2 as illustrated in Fig. 9 by way of example. As the injection pressure PB is raised with an increase in the amount of the injected material 44, the gap or distance between the mold 66 and the head cover 10 is increased, whereby the ease of leakage of the material 44 tends to increase. However, the leakage is prevented by an increase in the compressed air pressure PA to the required level PA2. As is apparent from the graph of Fig. 9, the required level PA2 is determined by experiment or simulation, so as to increase with the injection pressure PB detected in step S5. Step S13 is followed by step S14 to read the compressed air pressure PA again, and by step S15 to determine whether the detected compressed air pressure PA has reached the required level PA2 calculated in step S13. If an affirmative decision (YES) is obtained in step S15, step S19 is implemented to reset a counter C2 to "0", and the control goes back to step S4. Steps S4-S6 are repeatedly implemented until the affirmative decision (YES) is obtained in step S6. That is, the injection of the material 44 is continued until the injection pressure PB has reached the predetermined final level PB1. If the detected air pressure PA is lower than the required level PA2, a negative decision (NO) is obtained in step S15. In this case, step S16 is implemented to turn off the material feeding device 88 to stop the injection of the material 44, that is, to turn off the motor 89 to stop the elevating movement of the piston 50. Then, the control flow goes to step S17 to increment the counter C2, and step S18 to determine whether the content of the counter C2 has reached a predetermined number N2. The counter C2 is also reset to "0" immediately after the routine is initiated, or in step S19 described above. The content of the counter C2 represents a time lapse after the negative decision (NO) is obtained in step S15 for the first time, that is, a time length during which the compressed air pressure PA continues to be lower than the required level PA2. Steps S17 and S18 are provided to detect an abnormal rise of the compressed air pressure PA to the required level PA2, due to some trouble such as damage of the rubber tubes 70, 72, defect of the supply device 82 or poor connection of the tube 84 and connector 78. The predetermined number N2 may be a fixed number determined by the rate of rise of the air pressure PA while the supply device 82 and associated components are normal. Alternatively, the number N2 may be determined on the basis of the detected air pressure PA or injection pressure PB and according to a stored data map or equation representative of a predetermined N2-PA or N2-PB relationship. While the content of the counter C2 is smaller than the number N2, step S5 and the following steps are repeatedly implemented. If the detected air pressure PA has been raised to the required level PA2, that is, if the affirmative decision (YES) is obtained in step S15, the control goes to step S4 following step S19, whereby the material feeding device 88 is turned on again to resume the injection of the material 44. If the content of the counter C2 has reached the predetermined number N2, namely, if the predetermined time corresponding to the number N2 has passed without the air pressure PA reaching the required level PA2, the control flow goes to steps S11 and S12 to turn off the pressurized-fluid supply device 82 and turn on the ALARM light on the display 98. When the cavity 28 is filled with the material 44 injected by the material feeding device 88 and the CAVITY FULL light is lit on the display 98, the mold 66 is disconnected from the material feeding device 88 and pressurized-fluid supply device 82, while the mold 66 is clamped to the head cover 10 by the fixture 22. Then, the head cover 10 and mold 66 are introduced into the curing device 52 illustrated in Fig. 1(c), so that the material 44 filling the cavity 28 is cured. Since the material 44 has a relatively high viscosity value, the material 44 introduced into the cavity 28 will not be discharged through the injection passage 34 when the connecting tube 42 is disconnected from the connector 38. On the other hand, the connector 78 is automatically closed when the connecting tube 84 of the supply device 82 is disconnected from the connector 78. Therefore, the compressed air will not leak from the rubber tubes 70, 72 through the fluid passage, and the air pressure PA will not drop. When the mold 66 is removed from the head cover 10 after the curing of the material 44, the connector 78 is connected to the air bleeder joint 86 as shown in Fig. 10, so that the compressed air is forced out of the rubber tubes 70, 72 by the elasticity of the tubes 70, 72. The joint 86 is then disconnected from the connector 78, and the mold 66 removed from the head cover 10 is coated with a mold releasing agent at its groove 26, and returned to the mold clamping station of Fig. 1(a) for use with the next workpiece (head cover 10). In the present gasket fabricating system 90, the cavity 28 is pressure-tightly sealed by the rubber tubes 70, 72 which are elastically expanded by the compressed air introduced therein by the pressurized-fluid supply device 82 after the mold 66 is superposed on and clamped to the joining surface 14 of the workpiece in the form of the engine head cover 10. Further, the cavity 28 is filled with the material 44 by the material feeding device 88, and the material 44 is cured by the curing device into the gasket 12. Thus, the gasket 12 is simultaneously formed within the cavity 28 and fixedly attached to the fixing groove 16 formed in the head cover 10. Further, the rubber tubes 70, 72 elastically compressed against the joining surface 14 of the head cover 10 assure pressure tightness of the cavity 28 over the entire periphery of the cavity 28, without an excessive clamping force between the mold 56 and head cover 10, even if the joining surface 14 has some strain, deflection or buckling, or poor surface smoothness. Accordingly, the rubber tubes 70, 72 increases the yield ratio of the material 44. In the embodiment of Fig. 6, the injection of the material 44 is initiated only after the compressed air pressure PA in the rubber tubes 70, 72 has been raised to the initial level PA1 high enough to assure pressure-tight contact of the rubber tubes 70, 72 with the joining surface 14 and prevent leakage of the material 44. Further, the material supply device 88 once turned on is turned off to interrupt the injection of the material 44 if the air pressure PA is lower than the required level PA2 which is determined depending upon the injection pressure PB so as to prevent leakage of the material. Thus, the material 44 is injected while the air pressure PA is held higher than the required level PA2, so that the material 44 is prevented from leaking even when the injection pressure PB is considerably high during a terminal portion of the material injection period. Since the injection of the material 44 is started only after the air pressure PA is raised to the relatively low initial level PA1, the non-productive time is made shorter than in the case where the injection of the material 44 is started after the air pressure PA is raised to a comparatively high level corresponding to the injection pressure PB in a latter half of the injection period. In this respect, the time required to form the gasket 12 on the head cover 10 is significantly shortened. It will be understood from the foregoing description that a portion of the controller 92 assigned to implement steps S13-S16 (Fig. 8) constitutes means for controlling an operation to inject the material 44 while preventing leakage of the material 44. In the illustrated embodiment, the material feeding device 88 is temporarily held off while the air pressure PA is lower than the required level PA2. However, the delivery rate of the air compressor of the pressurized-fluid supply device 82 and/or the operating speed or torque of the motor 89 of the material feeding device 88 may be suitably adjusted so that the injection pressure PB of the material 44 and the air pressure PA will rise while maintaining or satisfying a suitable relationship that assures injection of the material 44 without leakage. Where a material feeding device comprising a pneumatically or hydraulically operated drive cylinder is used in place of the material feeding device 88, the pressure of the pressurized fluid applied to the drive cylinder may be adjusted to adjust the back pressure of the piston 50, rather than temporarily stopping the injection of the material 44. Further, the pressurized-fluid supply device 82 and the material feeding device 88 may be controlled to maintain the detected injection pressure PB below an upper limit, which is determined on the basis of the detected air pressure PA and according to a stored data map representative of a predetermined relationship between the pressures PA and PB, so that the material 44 will not leak at the pressures PA, PB. As described above, the present gasket fabricating system 90 is adapted such that the ALARM light is turned on without the material feeding device 88 being started if the actual air pressure PA is not raised to the initial level PA1 in a predetermined time after the pressurized supply device 82 is turned on, that is, before the count of the counter C1 reaches the predetermined number N1. Further, the material feeding device 88 is turned off and the ALARM light is turned on if a predetermined time has passed while the air pressure PA is held lower than the required level PA2 after the device 88 is turned on, that is, if the count of the counter C2 reaches the predetermined number N2 before the air pressure PA has reached the required level PA2. These arrangements permit early detection of any abnormality associated with the introduction of the compressed air into the rubber tubes 70, 72, such as damaging of the rubber tubes 70, 72, defects of the pressurized-fluid supply device 82 or abnormal connection of the connecting tube 84 and connector 78. Thus, the present system 90 is adapted to minimize the risk of leakage of the material 44, which would lead to reduced yield ratio of the material and defective gaskets 12 due to air in the mold cavity 28. It will also be understood that a portion of the controller 92 assigned to implement steps S3, S9 and S10 (Fig. 7) and steps S15, S17 and S18 (Fig. 8) constitutes means for providing an indication of abnormality associated with the introduction of the compressed air into the rubber tubes 70, 72. The initial and required levels PA1, PA2 are the threshold values used to detect the abnormality. Although the abnormality detection is effected both before and after the injection of the material 44 is started (in step S4), the detection may be effected only before or after the start of the material injection. That is, only a series of steps S3, S9 and S10, or only a series of steps S15, S17 and S18 may be implemented. While the present invention has been described in detail in its presently preferred embodiment with certain degrees of particularity in various aspects, it is to be understood that the invention is not confined to the details of the illustrated embodiment, but may be embodied otherwise. For instance, the principle of the present invention is equally applicable to the formation of the gasket 12 on any component other than the head cover 10, such as a transmission casing, an oil pan, and other parts which require a comparatively high degree of fluid- or pressure-tightness with respect to the mating part. Although the material feeding device 88 uses the feed cylinder 46 for forcing the material 44 into the cavity 28, the present invention may use other types of material feeding device, such as a device in which a screw having a helical vane or vanes is rotated by suitable drive means. While the gasket-forming groove 26 has a semi-circular cross sectional shape in the illustrated embodiment, the shape of the groove 26 may be modified as needed. Similarly, the cross sectional shape of the gasket-fixing groove 16 may be modified as needed.

Claims: A process for forming a gasket directly on a workpiece (10) having a joining surface (14) which has an annular gasket-fixing groove (16), said process comprising the steps of preparing a mold (66) including a body (68) having an annular gasket-forming groove (26) which cooperates with said gasket-fixing groove (16) to define a cavity (28) for forming said gasket, said body further having an injection passage (34) communicating with said gasket-forming groove; clamping said mold (66) to said joining surface (14) of said workpiece (10); injecting a material (44) for the gasket into said cavity (28) through said injection passage (34); curing said material injected in said cavity; removing said mold from said workpiece; said process being characterized by further comprising the steps of attaching inner and outer elastic tubes (70, 72) to said body (68) of said mold such that said inner and outer elastic tubes (70, 72) communicate with a fluid passage (76) of said body (68) and are disposed on inner and outer sides of said gasket-forming groove (26), respectively, so as to extend peripherally along said gasket-forming groove (26), said step of clamping said mold comprising clamping said body of said mold to said joining surface of said workpiece such that said inner and outer elastic tubes are held in elastic pressure-tight contact with said joining surface (14); connecting a pressurized-fluid supply device (82) to said fluid passage (76) for supplying said elastic tubes (70, 72) with a pressurized fluid; detecting a pressure of said pressurized fluid in said elastic tubes (70, 72); detecting an injection pressure of said material (44); and controlling at least one of said pressurized-fluid supply device (82) and a material feeding device (88) for injecting said material (44) into said cavity (28) through said injection passage (34) such that, during an operation of said material feeding device (88), the detected pressure of said pressurized fluid and the detected injection pressure of said material (44) increase so as to maintain a predetermined relationship therebetween without leakage of said material from said cavity (28). A process according to claim 1, further comprising the step of providing an indication of abnormality associated with the supplying of said pressurized fluid to said elastic tubes (70, 72), if the detected pressure of said pressurized fluid is lower than a predetermined threshold. A process according to claim 1 or 2, wherein said step of controlling at least one of said pressurized-fluid supply device (82) and said material feeding device (88) comprises calculating a required level (PA2) of the pressure (PA) of said pressurized fluid on the basis of said detected injection pressure (PB) of said material and according to said predetermined relationship, determining whether the detected level of the pressure of said pressurized fluid has been raised to the calculated required level, and stopping said step of injecting said material into said cavity until said detected level is determined to have been raised to said calculated required level. An apparatus for forming a gasket directly on a workpiece (10) having a joining surface (14) which has an annular gasket-fixing groove (16), said apparatus comprising: a mold (66) including a body (68) having an annular gasket-forming groove (26) which cooperates with said gasket-fixing groove (16) to define a cavity (28) for forming said gasket, said body further having an injection passage (34) communicating with said gasket-forming groove (26); a clamping device (22) for clamping said mold (66) to said joining surface (14) of said workpiece (10); a material feeding device (88) for injecting a material (44) for the gasket into said cavity (28) through said injection passage (34), characterized by a fluid passage (76) provided in said body (68); inner and outer elastic tubes (70, 72) attached to said body (68) such that said inner and outer elastic tubes communicate with said fluid passage (76) and are disposed on inner and outer sides of said gasket-forming groove (26), respectively, so as to extend peripherally along said gasket-forming groove (26); a pressurized-fluid supply device (82) connectable to said fluid passage (76) of said body (68), for supplying said elastic tubes (70, 72) with a pressurized fluid; a first pressure sensor (96) for detecting a pressure of said pressurized fluid in said elastic tubes (70, 72); a second pressure sensor (94) for detecting an injection pressure of said material; and a controller (92) for controlling at least one of said pressurized-fluid supply device (82) and said material feeding device (88) such that, during an operation of said material feeding device (88), the detected pressure of said pressurized fluid and the detected injection pressure of said material increase so as to maintain a predetermined relationship therebetween without leakage of said material from said cavity (28). An apparatus according to claim 4, further comprising means (98) for providing an indication of abnormality associated with the supplying of said pressurized fluid to said elastic tubes, if said controller (92) determines that the detected pressure of said pressurized fluid is lower than a predetermined threshold. An apparatus according to claim 4 or 5, wherein said controller comprises calculating means (S13) for calculating a required level (PA2) of the pressure (PA) of said pressurized fluid on the basis of said detected injection pressure (PB) of said material and according to said predetermined relationship, determining means (S15) for determining whether the detected level of the pressure of said pressurized fluid has been raised to the calculated required level, and stopping means (S16) for stopping said step of injecting said material into said cavity until said calculating means determines that said detected level has been raised to said calculated required level.

Inventors: MIWA HIROYUKI, MIZOBE TATSUYA, SUMIYOSHI MASAYUKI, MIWA, HIROYUKI, MIZOBE, TATSUYA, SUMIYOSHI, MASAYUKI, MIWA, HIROYUKI, TOYOTA JIDOSHA KABUSHIKI KAISHA, MIZOBE, TATSUYA, TOYOTA JIDOSHA KABUSHIKI KAISHA, SUMIYOSHI, MASAYUKI, TOYOTA JIDOSHA K.K.
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1994
Main classification: F16J15
IPC codes: B29C45, F16J15, C09K3